This epidemiologic study will examine the natural history of behavioral and social risk factors known to be associated with mortality and morbidity from cardiovascular disease, cancer, and other causes. Although much is known concerning the association between these risk factors and disease outcomes, little is known concerning the characteristics associated with changes in these risk factors. Even less is known concerning the characteristics associated with change in risk factors at different ages. Such information is critical if we are to understand most changes in risk factor levels which occur independently of formal interventions and the striking secular trends seen in the rates of many diseases. These issues will be studied using two cohorts of individuals chosen to be representative of Alameda County, California, in 1965 (n=6928) and 1974 (n=3118). Both cohorts received similar questionnaires in which they reported on a variety of behavioral, demographic, social, and psychological topics. Thus identical information is available for two cohorts separated in time by nine years. The 1965 cohort was also interviewed in 1974. This information will allow us to prospectively examine the reasons for change in behavioral and social risk factors such as cigarette smoking, alcohol consumption, relative weight, physical activity, and social network participation. In addition, we will be able to compare the changes prospectively observed within a cohort with those observed between two cohorts representing the same time. Such comparisons will help to clarify age, time of measurement, and birth cohort effects on risk factor levels and changes in risk factors. In particular, comparison of age and sex-specific risk factor levels in the 1965 and 1974 cohorts, along with the prospective information on changes between 1965-1974 within a cohort, will enable us to examine the age and sex-specific impact of major public health interventions between 1965 and 1974. These tasks will be accomplished using prospective analyses based on two cohorts chosen to be representative of an urban county, spanning a period in which there have been large changes in the levels of some risk factors. This will be carried out within the Alameda County Study, a 26-year-old investigation which has already contributed much to the epidemiologic foundations of primary prevention.